Final answer:
C) Acetic acid (CH3COOH)
The solution is buffered with acetic acid (CH3COOH) which is apparent from the small change in pH upon the addition of a strong base, which is a characteristic behavior of a buffer system.
Step-by-step explanation:
Five drops of 1.0M NaOH increase the pH of a solution from 3.0 to 4.6, and five additional drops only increase the pH to 4.7. These results indicate that the solution contains a buffer, which is a substance that helps maintain a stable pH in a solution when acids or bases are added.
Among the options presented, the solution is buffered with acetic acid (CH3COOH). This is evident because the addition of sodium hydroxide (a strong base) caused only a minimal change in pH, indicative of a buffer system at work, specifically one likely composed of acetic acid and its conjugate base, acetate.
At higher concentrations of this buffer, even greater volumes of NaOH would cause similarly modest shifts in pH, which is characteristic of the buffering action provided by weak acids like acetic acid and their salts.